Maps do more than tell us where we are. Rich with information elegantly arranged, they give us a way to assimilate our vast world. The clearer the map, the more confidently we set out to explore, looking for something it doesn’t show.In a few years, scientists will come out with a new map of a third of the sky, one that will go deeper and bring that depth into sharper focus than any survey has yet achieved. It will pinpoint in three dimensions the locations of 25 million galaxies and quasars, pulling back the curtains on the history of the universe’s expansion over more than half of the age of the universe.